rust17.hashmap

//1.HashMap<K,V>
//2.创建HashMap
//3.读取
//4.遍历
//5.更新
us std::collections::HashMap;

fn main() {
    //2.
    let mut scoures: HashMap<String,i32> = HahsMap::new();
    scores.insert(String::from("Blue"),10);
    scores.insert(String::from("Red"),20);

    let keys = vec![String::from("Blue"),String::from("Red")];
    let value = vec![10,20];
    let scores: HashMap<_,_> = keys.iter().zip(values.iter()).collect();//HashMap
    //当中的<_,_>表示这里有这样的值，但是我们不关心值的类型。
    //3.
    let k = String::from("Blue");
    //let v = scores.get(&k); //v = 10
    //不能够直接打印，因为get输出的为Option类型，需要使用模式匹配或者if let
    //println!("Blue = {}",v);
    if let Some(v) = scores.get(&k) { //get 返回一个Option类型
        println!("Blue = {}",v);
      }
    
    let k = String::from("yellow");
    let v = scores.get(&k);
    match v {
        Some(value) => println!("Blue = {}",value),
        None => println!("None"),
      }
    
    //4.遍历:顺序是任意的
    for (key,value) in &scores {
        println!("{},{}",key,value);
      }
    //5.
    //直接插入
    let mut ss = HashMap::new();
    ss.insert(String::from("one"),1);
    ss.insert(String::from("two"),2);
    ss.insert(String::from("three"),3);
    //同名会覆盖
    ss.insert(String::from("one"),3);
    println!("{:?}",ss);

    //键不存在时插入
    let mut ss1 = HashMap::new();
    ss1.insert(String::from("one"),1);
    ss1.insert(String::from("two"),2);
    ss1.insert(String::from("three"),3);
    ss1.entry(String::from("one")).or_insert(3);//只有键值不存在才插入
    println!("{:?}",ss1);
    
    //根据旧值来更新一个值
    let text = "Hello world wonderful world";
    let mut map = HashMap::new();
    for word in text.split_whitespace() {
        let mut count = map.entry(word).or_insert(0);
        *count += 1;
      }
  }